JUST PURCHASED A DISCOVERY ONE 200 DIESEL.PROBLEM IS THE HEATER WILL NOT BLOW ONTO THE SCREEN.BLOWER WORKS,AIR CON WORKS.ALL LEVERS ARE WORKING AND I HAVE REMOVED THE FRONT PANEL AND NOTHING HAS COME OF.AM I MISSING SOMETHING SIMPLE,PLEASE HELP BECAUSE THERES NOTHING WORSE THAN A SCREEN THAT WONT DEMIST...